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(SPACE.com) -- A European probe bearing down on the planet Venus is set for a Tuesday arrival to take a close look at the world's soupy atmosphere.

After five months of spaceflight, the European Space Agency's (ESA) Venus Express orbiter is expected to fire its main engine in a nearly hour-long maneuver to begin its planet-watching duties.

"I don't dare get too excited because we have to be calm if there are any problems," Venus Express project manager Don McCoy told SPACE.com. "It will feel good once we know we're in orbit around the planet."

The ESA launched the $226 million (220 million Euro) Venus Express mission spaceward in November 2005 on what the space agency has billed its fastest mission to fly.

Not since NASA's Magellan mission ended with the spacecraft's death plunge into the Venusian thick atmosphere in 1994 has the planet had a dedicated orbiter around it.

"It's getting very close and everything is working well, so that is comforting," said Hakan Svedhem, Venus Express project scientist, in a telephone interview.

The 2,799-pound (1,270-kilogram) Venus Express spacecraft is expected to fire its main engines for 50 minutes beginning at 3:17 a.m. EDT (0717 GMT) Tuesday to place itself on the proper orbital trajectory.

By the maneuver's end the spacecraft is expected to be flying in an orbit that reaches 248 miles (400 kilometers) above the Venusian surface at its low point and about 217,479 miles (350,000 kilometers) at the high end, mission managers said.

"It's a very eccentric orbit," said McCoy, adding that it should take Venus Express a full nine days to complete its first orbit while observing the planet.

"It's the only time during the entire mission that we'll be able to see the entire planetary disk."

Unveiling Venus

Venus Express carries seven primary instruments, many of which were spares left over from previous ESA missions such as the agency's Mars Express and comet-bound Rosetta programs, to peel back the layers of the Venusian atmosphere.

Researchers hope the spacecraft will unveil the source of Venus' dense, turbulent and toxic atmosphere.

"We think that volcanism is the mechanism that would produce that atmosphere," Svedhem said. "And if we find that this is the case, well that I think would be very exciting."

Svedhem and his colleagues also hope to better understand how trapped carbon dioxide, water vapor and sulphuric aerosol gases factored into the "greenhouse effect" that appears to superheat Venus' atmosphere to an average temperature of about 869 degrees Fahrenheit (465 degree Celsius).

Venus Express is expected to begin its primary science mission -- a 15-Earth month period that translates into two of Venus' long sidereal days -- in June after a series of maneuvers to reach its final operational orbit.

"It's just straight propulsion," McCoy said of the orbital posturing, adding that unlike NASA's Mars Reconnaissance Orbiter -- which is currently using Mars' atmosphere to shape its orbit in a process called aerobraking -- Venus Express will rely solely on its engines. "It's lot faster than aerobraking and, in that sense, it's easier."

Venus Express' transit to its target planet required less of the probe's 1,256 pounds (570 kilograms) of fuel than anticipated, allowing for some leeway in the process, ESA officials said.